Method of preparing a wound dressing

ABSTRACT

A method of preparing a wound dressing includes coating a support layer with an adhesive layer and forming a pattern of depressions in the adhesive layer on an edge portion of the wound dressing, with the pattern of depressions being in the adhesive layer and not penetrating the support layer. The method includes forming a plurality of through-going holes in a central portion of the wound dressing, with the through-going holes penetrating both the support layer and the adhesive layer and each of the plurality of through-going holes at least as large in the support layer as in the adhesive layer.

This invention relates to a medical adhesive dressing. Morespecifically, the present invention is directed to a method ofmanufacturing a medical adhesive dressing comprising a backing film, apatterned adhesive layer and an absorbent pad.

BACKGROUND

An adhesive dressing is typically composed of an adhesive which iscoated on a backing layer and the dressing is typically further providedwith an absorbent layer e.g. in the form of an absorbent pad. Such anadhesive dressing should have adhesion suitable for firmly adhering thedressing to the skin and subsequently easily removing it from the skin.Furthermore, the dressing should have high water vapour permeability toavoid skin damage because it is directly attached to the skin, in whichhigh water vapour permeability can promote wound healing.

Conventionally, the adhesive of dressings has the pressure-sensitiveadhesive coated onto an entire surface of the backing layer. Thus,conventional dressings are disadvantageous in terms of low water vapourpermeability, due to the coated adhesive per se, regardless of the watervapour permeability of the backing layer. That is, even though a backinglayer having high water vapour permeability is used, the adhesive coatedon the entire surface of the backing layer may prevent water vapourpermeation, whereby the water vapour permeability of the dressing isreduced.

Wound dressings comprising soft adhesives, such as for example silicone,polyurethane or acrylate based adhesives are popular due to theirsoftness. These soft adhesives are often solvent based and manufacturingdressings with these usually includes a drying or curing step andlimited opportunity of modelling the adhesive after these steps.

Most of the known coating methods with such adhesives can only coat oneuniform thickness at one time and the amount of waste in the process maybe substantial.

If the absorbent pad is directly attached to the middle of the coatedbacking layer, the adhesive area between the absorbent pad and backinglayer is largely wasted as it is not used for adhesion to the skin asintended. The adhesive, though formulated for good properties for skincontact, may not have the optimal properties for attaching the absorbentpad. For attachment of the absorbent pad, a cheaper or more effectiveadhesive or attachment method may be used.

An exposed absorbent pad on a backing layer requires good anchorage tothe backing layer, especially when wet and heavy due to being soakedwith exudate. By good anchorage is meant that absorption of moisturedoes not cause the absorbent pad and the backing layer to delaminate.

An exposed absorbent pad surface facing the wound side maximises theexudate absorption when in place. However, longer term placement (suchas for a period longer than 3-5 days) on the wound may lead to ingrowthof tissue of the healing wound onto the absorbent core surface or moredifficult removal, which in turn irritates the wound.

To overcome the removal problem, contact layers of less adhering natureare known. These contact layers are often thin films or gel layershaving perforations to expose the absorbent core.

Another function of the contact layer may be to support and hold theabsorbent core in position.

There is a need to simplify and improve the processes of dressingconstruction with different patterns and thicknesses of the differentparts of the adhesive layer. There is a need to maximize the contactarea to skin but minimize the coverage of the backing film.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for producingan adhesive wound dressing with different patterns and thicknesses ofthe different parts of the adhesive layer.

Yet an object is to provide a method of producing an adhesive dressing,with reduced waste of adhesive.

An object is to provide a skin-friendly dressing with good moisturehandling properties and good adherence to the skin.

An object is to provide an adhesive dressing with variable thickness ofthe adhesive layer.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates an embodiment of the invention in cross-section(exploded view).

FIG. 2 discloses the embodiment in perspective (exploded view).

DETAILED DESCRIPTION OF THE INVENTION

In a first aspect, the invention relates to a method of preparing anadhesive wound dressing, the dressing comprising a central portion andan edge portion, the method comprising the steps of: Providing a supportlayer, drawing the support layer into a mold, dispensing a portion ofuncured adhesive over the mold, distributing the uncured adhesive in themold, removing excess adhesive, curing the adhesive thereby providing anadhesive laminate consisting of the support layer and the curedadhesive, detaching the support layer from the mold, providing thecentral portion of the adhesive laminate with a plurality through-goingholes, placing an absorbent pad on the non-adhesive side of the centralportion of the support layer and laminating a backing layer to theabsorbent pad and an edge portion of the support layer.

In a second aspect the invention relates to an adhesive wound dressingcomprising a central portion and an edge portion, the dressing comprisesa support layer being at least partly coated with an adhesive layer thusforming an adhesive laminate, the support layer of the edge portion ofthe dressing being continuous and the edge portion of the dressing beingprovided with a pattern of depressions in the adhesive layer and thecentral portion being provided with a plurality of through-going holesin the adhesive laminate, the dressing comprises an absorbent padcovering the central portion of the non skin facing surface of thesupport layer, and a backing layer being laminated to the absorbent padand the edge portion of the support layer.

The edge portion of the dressing is surrounding the central portion toform an adhesive flange circumferending the central portion with theabsorbent pad. Such construction is often called an island dressing. Thedressing may be produced in many different sizes and shapes.

The width of a dressing may be from 2-40 cm, such as 5-35 cm, 7.5-30 cm,10-20 cm or even 10-15 cm. The width of the dressing is measured at thebroadest dimension of the dressing; a rectangular dressing having thedimensions of 10×20 cm has a width of 20 cm.

The edge portion may have a width of 1.5-6 cm, such as 2-5 cm, 2.5-4.5cm or even 2.5-4 cm. The width of the edge portion is measured from theedge of the dressing to the outer edge of the absorbent pad of thecentral portion.

The absorbent pad may have a width of 2-30 cm, such as 3-25 cm, 3-20 cm,3.5-15 or even 4-13 cm.

The edge portion of the support layer being continuous should beunderstood as the layer is not provided with holes or apertures.

Molding the adhesive layer on a support layer makes it possible tooptimize the permeability by reducing the thickness of the adhesivelayer or even make sections without adhesive within the dressing. It isalso possible to obtain different thicknesses of the adhesive layerwithin the same product. Different thicknesses provide differentproperties of the dressing, for example may a higher thickness at theedge portion provide a better adhesion or it may provide increasedstiffness to the product. Other sections of the product may have reducedthickness in order to save material or to provide higher permeabilityand flexibility.

The thickness of the adhesive layer at the edge portion may be 150-500μm, such as 200-450 μm, 250-450 μm or even 300-400 μm. The thickness ofthe adhesive layer at the central portion may be 75-250 μm, such as100-200 μm, 125-175 μm or even 150 μm.

In one embodiment according to the first or second aspect of theinvention a pattern of depressions may be molded in the edge portion ofthe adhesive layer. The depressions of the edge portion may penetrate apart of the adhesive layer or they may pass through the entire adhesivelayer. The support layer at the depressions is not penetrated butremains intact. If the depressions penetrate the entire thickness of theadhesive layer, a neglectable amount of adhesive may however be presentat the support layer at the bottom of the depressions. The depressionsmay enhance the permeability of the dressing as well as they mayfacilitate increased flexibility due to a thin layer of adhesive in thedepressions. When the molded adhesive and the support layer are combinedwith a backing layer, it may be preferred to have depressions in themolded adhesive layer. By the here described molding process, it ispossible to mold the adhesive layer so there are no or a reduced amountof adhesive at the sections where the depressions may be made.

At the edge portion of the dressing the double layer of films (backinglayer and support layer) may provide a reservoir effect. The moisturepassing through the adhesive coated support layer may be temporarilytrapped in a void volume/the space between the support layer and thebacking layer and subsequently evaporate through the backing layer. Inthis way the moisture will be removed fast from the skin surface andinto this reservoir between the layers from where it may evaporatethrough the backing layer.

The support layer may be stretched during the molding process and thestretching may facilitate a higher permeability of the support layer andthereby easier passage of moisture away from the skin.

By stretching of the support layer the thickness of the layer may bealtered for example from a starting thickness of 15-25 μm to a thicknessof around 10 μm where it is thinnest. This may result in differentiatedpermeability of the layer. The support layer may be stretched up to100%.

In one embodiment the void volumes between the support layer and thebacking layer may comprise salt or other components that may enhanceosmosis.

Wound dressings having different thickness of the adhesive layer, e.g.in the form of bevelled edges and indentations, are usually producedwith a thermoplastic, non-curable adhesive such as a traditionalhydrocolloid adhesive. Such dressings may be produced by coating auniform thickness layer of adhesive on a film and then, by adding heatand pressure, forming the desired configuration of the dressing. Apartfrom being confined to use thermoplastic adhesives, this method ofproduction also produces substantial amount of waste.

The through-going holes of the central portions may be made by punching,cutting or by applying high frequency mechanical vibrations, for exampleas disclosed in WO 2010/061228. By through-going is herein meant thatthe holes pass through both the support layer and the adhesive layer.

When making holes by applying high frequency mechanical vibrations, thesupport layer at the holes may melt to adhere to a temporary releaseliner (a release liner being present during the production process, butremoved or substituted with a release liner for the final product). Whenthe temporary release liner is removed, the residues of the supportlayer may be removed with it and the holes appear less frayed at theedge. The temporary release liner may be made from polyethylene (PE).

The central portion of the dressing may be provided with depressionsduring the molding process of the adhesive and the through going holesare then subsequently made in the depressions. This may save adhesivematerial in the process.

Through going holes may be arranged in a regular or random array,typically separated by 0.5 to 10 mm, such as 1-7 mm, such as 2-5 mm. Thenumber of holes per dressing may be between 1 and 200, such as between 3and 150, such as between 5 and 100, such as between 5 and 50 or evenbetween 5 and 20. The number of through going holes per cm² of thecentral portion of the dressing may be 1-10, such as 1-7, such as 1-5 oreven 2-5.

The holes in the central portion facilitate easy access for the woundexudates to enter into the absorbent pad. The holes may have a diameterof 0.5-10 mm, 1-8 mm, 1-5 mm, 1.5-5 mm, or even 2-4 mm.

The support layer may be any suitable layer being water impermeable butvapour permeable. A suitable support layer may be a polyurethane film.

The absorbent pad may be a uniform material or it may be a composite,for example in the form of a layered construction comprising layers ofdifferent texture and properties. The absorbent pad may comprise foam,cellulose, super absorbent particles or fibres or mixtures thereof. Theabsorbent pad may comprise a layer of foam facing the wound.

The absorbent pad may comprise a polyurethane foam.

The absorbent pad may comprise a super absorbing layer. The superabsorbent layer may be combined with a layer of foam.

The absorbent pad may be bevelled in order to facilitate a smoothtransition between the absorbent pad and the surrounding edge portion.Furthermore, the bevelling may reduce the risk of pressure marks.

The adhesive may be a thermoset, curable adhesive. An example of suchadhesive may be a silicone based adhesive. The adhesive may be atwo-component system. Preferably, the adhesive contains no solvent.Preferred adhesives include polyurethane, acrylic, silicone orpolyethylene or polypropylene oxide based cross-linking types asdescribed in patent WO2005/032401. Or the adhesive may be a hotmelttype, which initially is heated to flow and subsequently cooled to gelor crosslink. Instead of curing upon cooling, the adhesive may in someembodiments cure upon application of thermal energy.

By molding the adhesive it may be possible to achieve beveled edges ofthe adhesive layer, even though the adhesive is a thermoset adhesive.Such adhesives may otherwise be difficult to produce in layers ofvariable thickness as they cannot be formed by exposing them to heat andpressure.

The thickness of the adhesive layer may be uniform or it may vary overthe dressing, for example the adhesive layer in the central portion maybe thinner than the thickness of the edge portion or vice versa. In thisway, the adhesive layer may be tailor made for the dressing.

The support layer may be stretched before entering the mold. Thestretching of the support layer in specific areas facilitates a higherpermeability. The stretching of the support layer can also be used tochange other properties of the layer. Stretching can be orientated sothe layer will be more flexible in one direction than in another.

Stretching of the support layer and/or backing layer may also be usedfor obtain more space for expansion of the absorbent pad beingintegrated in the wound dressing. If either the support layer or thebacking layer is stretched during the manufacturing of the dressing, itmay be possible to provide more space for expansion of the absorbentpad.

The process, first preparing the support layer with adhesive coating andcentral holes, and then assembling the dressing with backing layer andabsorbent pad in between render it possible to achieve a wound dressingwith tailor made depressions, holes and thickness of the adhesive layer,and where the absorbent pad is entrapped between the support layer andthe backing layer. The wound contacting surface will reduce risk ofingrowth of the wound but still facilitate rapid absorption of woundexudates due to the presence of the perforated adhesive layer.

The method of the invention combines the advantages of molding adhesivewafers e.g. for wound care with a solution where the central absorbentpad is enclosed between a backing film and an adhesive coated supportlayer. Hence it is possible to produce an absorbing wound care productwith reduced waste and with a bacteria proof backing layer on one sideand an adhesive coated support layer on the other.

The adhesive coated support layer of the dressing may be molded in anendless loop of molds. Afterwards holes may be made in the centralportion in order to facilitate high permeability. An absorbent pad isplaced on the non-adhesive side of the adhesive coated support layer. Ahigh permeable backing layer is placed on top of the combination ofsupport layer and absorption layer and the backing layer and the supportlayer are joined together, thereby enclosing the absorbent pad. Thebacking layer is preferably the same size as the support layer. Arelease liner protecting the adhesive surface before use may be added tothe dressing.

The molding process provides the advantage of differentiated thicknessof the adhesive layer in the same dressing and it will render itpossible to design all kinds of dressing shapes without generatingadhesive waste, as the adhesive is only added to the product in thecavity of the molds.

In one embodiment, the molding tool is cylindrical/drum-shaped, and thesupporting surface is arranged to convey the liquid adhesive from anapplication area to a molding area in which the molding tool engages theadhesive. Moreover, the step of providing the adhesive and the step offorcing the molding tool into the adhesive may be performedconcurrently.

The adhesive is in a liquid form during coating and becomes aform-stable mass upon coating. The adhesive may be a two-componentsystem. Preferably, the adhesive contains no solvent.

In the context of the present invention the term “curing energy” shallbe understood as any energy source suitable for curing the adhesive.Examples are thermal energy (heat), UV-radiation, IR-radiation ormicrowaves.

The absorbent pad and/or the adhesive layer may contain activeingredients, such as ibuprofen, paracetamol, silver compounds or othermedically active ingredients adapted to reduce pain or to improve thehealing of a wound. In one embodiment the absorbent pad comprises asilver compound with antimicrobial properties.

In one embodiment the dressing may comprise a silver compound in theform of a silver sodium hydrogen zirconium phosphate complex.

During the manufacturing process the adhesive material may reach aform-stable state without being fully reacted.

In the context of the present invention the term “form-stable” meansthat the material retains its shape under normal conditions, i.e. in thetemperature range 25 to 130° C.

Full reaction or gelation may occur at a subsequent step of post-curingat which curing energy such as thermal energy may be provided toaccelerate full reaction.

In order to achieve the predetermined pattern of the edge portion of theadhesive layer, the molding tool may comprise protrusions extending awayfrom a base level of the molding tool i.e. towards the backing filmduring the molding process. It will be appreciated that the depressionswill be defined by said protrusions, as the protrusions duringapplication of pressure to the molding tool during molding will forcethe adhesive into the spaces defined between the protrusions of themolding tool.

The permeability of the central portion of the dressing may be at least5000 gsm/24 h (gsm=grams per m²).

The permeability of the edge portion of the dressing may be at least1000 gsm/24 h (gsm=grams per m²). The permeability of the dressing ismeasured by the method of the international standard EN 13726-2.

The absorbent pad may be adhered to the backing layer e.g. by welding inorder to avoid delamination when wet.

The method opens up for producing a wide variety of shapes of thedressing with very little waste of material. Examples of dressing shapesmay be rectangular, circular, elliptic or triangular.

DETAILED DESCRIPTION OF THE DRAWING

The invention will now be described in further detail with reference tothe figures.

In FIGS. 1 and 2 are shown an embodiment of the invention in explodedcross-section and perspective view.

The dressing comprises a central portion (1) and an edge portion (2)surrounding the central portion (1). A support layer (3), e.g. in theform of a polyurethane film, is coated with a silicone adhesive layer(3) on the skin-facing surface. The edge portion of the adhesive layer(4) is provided with a pattern of depressions (5), the depressions (5)being in the adhesive layer (4) but not penetrating the support layer(3). The central portion of the adhesive coated support layer (3,4) isprovided with a pattern of through going holes (6), the through-goingholes (6) penetrating both the adhesive layer (4) and the support layer(3). On the non-adhesive side of the support layer is an absorbent pad(7), covering the central portion (1). The absorbent pad (7) may forexample be a polyurethane foam sheet. The absorbent pad (7) may bebevelled at the edge portion. A backing layer (8) of substantially thesame dimensions as the support layer (3) is laminated to the absorbentpad (7) and the edge portion (2) of the support layer (3). The backinglayer (8) may be a polyurethane film of the same type as the supportlayer (3). The skin-facing adhesive surface of the dressing may beprotected by one or more release liners (9) before use.

1. A method of preparing a wound dressing, the method comprising:coating a support layer with an adhesive layer; forming a pattern ofdepressions in the adhesive layer on an edge portion of the wounddressing, with the pattern of depressions being in the adhesive layerand not penetrating the support layer; forming a plurality ofthrough-going holes in a central portion of the wound dressing, with thethrough-going holes penetrating both the support layer and the adhesivelayer and each of the plurality of through-going holes at least as largein the support layer as in the adhesive layer; placing an absorbent padover the central portion on a non-skin facing surface of the supportlayer; and laminating a backing layer to the absorbent pad and the edgeportion of the support layer of the wound dressing.
 2. The method ofclaim 1, comprising coating the support layer with a thermoset, curableadhesive layer.
 3. The method of claim 1, comprising placing anabsorbent foam pad over the central portion on the non-skin facingsurface of the support layer.
 4. The method of claim 1, comprisingplacing super absorbing pad over the central portion on the non-skinfacing surface of the support layer.
 5. A method of preparing anadhesive wound dressing, the adhesive wound dressing having a centralpart and an edge portion, the method comprising the steps of: a.providing a support layer; b. placing the support layer into a mold; c.dispensing a portion of uncured adhesive into the mold and onto thesupport layer; d. distributing the uncured adhesive in the mold; e.removing an excess of the uncured adhesive from the mold; f. curing theuncured adhesive and providing a cured adhesive; g. removing the supportlayer and the cured adhesive from the mold; h. forming a pluralitythrough-going holes in the central part of the wound dressing; i.placing an absorbent pad on a non-adhesive side of the central part ofthe wound dressing; and j. laminating a backing layer to the absorbentpad and to the edge portion of the support layer.
 6. The method of claim5, comprising forming a pattern of depressions in the adhesive layer. 7.The method of claim 5, comprising forming a pattern of depressions inthe adhesive layer, with the pattern of depressions being in theadhesive layer and not penetrating the support layer.
 8. The method ofclaim 5, comprising dispensing a portion of uncured silicone adhesiveinto the mold and onto the support layer.
 9. The method of claim 5,comprising forming a plurality through-going holes in the central partof the wound dressing by applying high frequency mechanical vibrationsto the cured adhesive.
 10. The method of claim 5, comprising forming aplurality through-going holes in the central part of the wound dressing,with each of the plurality of through-going holes having a diameter in arange from 1-10 mm.
 11. The method of claim 5, comprising placing a foamabsorbent pad on the non-adhesive side of the central part of the wounddressing.
 12. The method of claim 5, comprising curing the uncuredadhesive and providing the cured adhesive with a thickness measured atthe central part of the wound dressing that is thinner than a thicknessof the cured adhesive measured at the edge portion of the wounddressing.
 13. The method of claim 5, further comprising stretching thesupport layer prior to placing the support layer into the mold.